Gustafson turned professional in 1992 whilst studying marketing, economics and law at Aranasskolan & Komvux University in Sweden.[6] In the next three years she played 12 Telia Tour and four Ladies European Tour tournaments. On the Telia tour she had six top ten finishes. Her best finish on the LET was a 22nd at her home tournament in Sweden.[7][8][9]

1995 saw her join the Ladies European Tour gaining two top 10 finishes in 13 starts.[10] 1996 was her first full year on the Ladies European Tour. She gained her first professional wins, winning once on the Telia Tour at the Rörstrand Ladies Open[11] and once on the Ladies European Tour at the Déesse Ladies Swiss Open.[12] In 1997 she earned her first win on the Ladies Asian Tour at the Thailand Ladies Open[13] and finished T40th at LPGA Q School to earn non-exempt status for 1998.[6]

In 1998 Gustafson won twice on the LET at the Donegal Irish Ladies' Open and at the Marrakech Palmeraie Open, finish second on the Order of Merit and was voted Waterford Players' Player of the Year.[3] She also played four times on the LPGA tour, recording a second-place finish at the co-sanctioned Women’s British Open.[6] She also won the Telia Tour Finale[14] and made her debut in the Solheim Cup, replacing the injured Trish Johnson at the last minute.[15] During 1999, Gustafson played on both the LPGA and Ladies European Tours. Her best result was a tie for 2nd at the Ladies' German Open on the Ladies European Tour.[3]

2000 was a breakthrough year for Gustafson. She got her maiden win on the LPGA at the Chick-fil-A Charity Championship,[16] and added a second LPGA title at the co-sanctioned Women’s British Open.[17] She had two other wins in Europe at the Ladies Italian Open and at the Waterford Crystal Ladies Irish Open,[18] and partnered with Carin Koch to win the inaugural TSN Ladies World Cup Golf.[19] She also won 2 and a half out of a possible four points in Europe's Solheim Cup victory at Loch Lomond.[3] The year ended with Gustafson topping the Evian Order of Merit and official Evian moneylist, being voted Swedish Player of the Year by the Association of Swedish Golf Writers and becoming Players' Player of Year'.[18][20]

In 2001 Gustafson won once on both the LPGA Tour at the Subaru Memorial of Naples[21] and Ladies European Tour at the AAMI Women's Australian Open[22] crossing the LPGA Tour career $1million earnings mark. The defence of her LPGA title ended with her losing in a playoff to Annika Sörenstam.[23] In 2002 she played seven LET events, posting four top 10 finishes, ending the season with one victory at the Biarritz Ladies Classic[24] and 3rd place in the Order of Merit as well as winning the Vivien Saunders Stroke average trophy.[3] She made 15 of 20 cuts on the LPGA, with her best finish an 11th.

In 2003 she won three out of eight LET events[25][26][27] and secured another LET Order of Merit title. She also won her third LET Players' Player of the Year award and the Vivien Saunders Stroke Average trophy.[28] She won the Samsung World Championship on the LPGA tour,[29] her 4th LPGA win, crossing the $2million LPGA Tour career earnings mark. She became the first woman to compete in a men's Japan Golf Tour event,[30] and was part of the winning European Solheim Cup team in her native Sweden.

During 2004 Gustafson struggled with illness due to deep vein thrombosis in her leg.[3] Her best finish of the year was a tie for third on the LPGA tour where she led the tour in driving distance at 270.2 yards. At the start of 2005, Gustafson represented Sweden with Carin Koch in the 2005 Women's World Cup of Golf in SA.[31] Three LET events in 2005 yielded a second-place finish at the Weetabix Women's British Open and 3rd place on the LET Money List. On the LPGA Tour she had seven top 10 finishes and tied her career low round of 64 at the Wendy's Championship for Children.[3] Gustafson made her 5th appearance in the Solheim Cup.[32] and was a member of the International Team in the inaugural Lexus Cup.[33]

In 2006, Gustafson married former LPGA commissioner Ty Votaw,[35] who left his post following the 2005 Solheim Cup. They divorced in January 2010.[36] Gustafson has a severe stuttering problem and rarely speaks to the media. During the 2011 Solheim Cup she made an exception and spoke on-camera with Golf Channel.[37]

^ The Women's British Open replaced the du Maurier Classic as an LPGA major in 2001
^^ The Evian Championship was added as a major in 2013
DNP = did not play
CUT = missed the half-way cut
"T" = tied
Yellow background for top-10.